1. Field of the Invention
The present invention relates to an electronic seal. In particular, the present invention relates to an RFID electronic seal. The present invention also relates to a system using the RFID electronic seal for tracking cargo.
2. Description of the Related Art
To fulfill the demand of logistics, the goods after being manufactured are put into the supply chain. The most important information to both the supplier and the customer is the location of the goods in the supply chain management. Current cargo tracking systems use an IC (integrated circuit) card and GPS (global positioning system) or mobile phone system to monitor the location of the cargo truck, providing the cargo owner with the information of the number of the license plate of the cargo truck, the code number of the cargo container, the current location of the cargo truck, etc. It is, however, impossible to know whether the cargo container is opened and/or the cargo in the cargo container is stolen or switched, or to prevent such events.
RFID (radio frequency identification) electronic seals are proposed to solve the above problems. A typical electronic seal has a structure similar to a combination lock to seal the rear door of a cargo truck, allowing the owner of the cargo to acquire the required information. The owner will notice in real time after unauthorized breakage of the RFID electronic seal. An active type electronic seal (e.g., SaviTag 654 manufactured by Savi Technology Inc. of California) comprises a battery unit for transmitting signals through antennae. The transmitting distance of the active type electronic seal is about 50 meters, which is much longer than that of a passive type. However, the cost of the active type electronic seal is relatively high. Further, to provide real-time monitoring, the active type electronic seal is mounted to the rear door of a cargo truck that has a cab in which a reader is mounted, with the reader being connected to GPS or a mobile phone system. Transmission of the signals from the rear of the cargo container to the reader in the cab is interfered by the cargo container made of metal. A solution to this problem is to install readers along the route along which the cargo truck moves, resulting in a considerable expenditure. A passive type RFID electronic seal, though cheaper, has a small transmission distance and also fails to overcome the interference from the metal cargo container when used on a cargo truck.